Suppose, we need to construct a triangle of whose two given sides are 'a' cm and 'b' cm and three given angles are x, y and z.

 
Step 1: Draw PQ = a cm.
Step 2: Construct angle measuring x° at point Q.
Step 3: with Q as centre and radius equal to b cm cut an arc to meet at R.
Step 4: Construct an angle measuring y° at point R.
Step 5: Construct an angle measuring z° at P.
Step 6: The point of intersection of both the lines is the required point. Let this point be S. 
Thus, fourth point is plotted using lines made by any two angles.